Western Australia in June 2012: An average month for most of WA

Rainfall

Rainfall during June 2012 was near average for much of WA. Above to very much
above average rainfall was observed in the South Coastal district, Central West,
eastern parts of the Central Wheat Belt, the southern Gascoyne and parts of
the Goldfields. Most of the Southwest Land Division (SWLD) saw near average
totals. In what is typically a dry time of year in the north of WA, areas of
above average rainfall were observed in small parts of the Pilbara, particularly
around the Karratha area, while large areas of below average rainfall were observed
in the Kimberley and central Interior.

When averaged across the state as a whole, June 2012 rainfall was near average.
The Lower Southwest (southwest a line from Jurien Bay to Bremer Bay) also observed
near average rainfall during June 2012; however, for the year to date (January
to June) rainfall has been below average, primarily due to a very dry autumn
(the 7th driest). Comparable rainfall records commenced in 1900.

June 2012 saw frequent rainfall in western and southern parts of the SWLD,
with some sites recording rainfall on over 20 days in the month. A series of
low pressure systems and cold fronts brought a number of significant weather
events to the SWLD, which not only brought moderate to heavy rainfall, but also
damaging winds and significant storm surges during the first half of the month,
particularly between the 7th and 13th. The second half of the month saw mainly
light to moderate rainfall events in the SWLD, with the passage of several more
moderate cold fronts.

A slow moving trough and low pressure system moved over the SWLD at the end
of May and the start of June, bringing moderate to heavy rainfall and thunderstorms
to southern and eastern parts of the SWLD and adjacent Goldfields. A number
of locations in the Southwest and South Coastal districts registered daily rainfall
totals over 80 mm during the first two days of June. Warner Glen in the Southwest
district recorded a total of 106.4 mm on the 1st, which was its wettest day
in its 63 years of record. Tamaru in the South Coastal received a daily total
of 116.2 mm on the 2nd, which was the highest daily total for any month in its
47 years of record, and also the heaviest daily rainfall event in the SWLD since
late last year when 125.6 mm was recorded at Williams in the Great Southern
on 13 December 2011. Several sites in the South Coastal district recorded their
highest June total rainfall with the combination of this event and above average
rainfall for the remainder of the month.

A low off the WA west coast on the 6th brought extensive cloud to much of the
state resulting in areas of rain over much of western WA. Heavy falls were observed
in the Pilbara and Central West, with totals over 50 mm reported near Roebourne,
whilst highest June daily falls in 10 years were reported at some Pilbara sites.

A rapidly deepening tropical low off the northwest coast moved near the west
coast during the morning and crossed the Southwest district during the afternoon
on the 10th. The system brought very windy conditions to the Lower West, Southwest,
South Coastal, and Great Southern districts. The highest recorded wind gust
during the event was 146 km/h at Cape Naturaliste, which is the strongest wind
gust observed at the site in almost 10 years or record, and the 4th strongest
wind gust on record in Western Australia in the May to August period. Widespread
property damage was reported in western parts of the SWLD with a significant
number of trees downed, and 800 power lines southwest of a line from Geraldton
to Ravensthorpe damaged. More than 170,000 homes lost power and it took several
days for power to be restored to all residents in the region. A significant
storm surge with minor coastal inundation was reported along the SWLD west coast.
Some moderate to heavy falls were observed in the west Pilbara, west Gascoyne,
and western parts of the SWLD during the event and a few locations in the northern
Central West recorded their wettest June day on record as the result.

Most of WA, apart from the Kimberley, experienced a wet day on the 11th as
a cold front moved through the SWLD and a cloudband moved across northwest and
central parts of the state. Moderate to heavy falls were mainly confined to
southern parts of the SWLD, whilst the west coast parts of the division endured
more severe winds and a storm surge event.

A rapidly developing cold front and deep low pressure system moved through
the SWLD during the afternoon and evening of the 12th, and through central and
eastern parts of southern WA on the 13th. Widespread rainfall was recorded through
the SWLD, with heavy falls in the 40 mm to 60 mm range in the Southwest and
Lower West districts. Thunderstorms, moderate to heavy rainfall, and severe
wind gusts were reported in the SWLD, particularly in the Southwest and neighbouring
districts, as further roof damage was reported to buildings, trees were uprooted,
and additional power lines were downed. Another storm surge occurred although
it was weaker than previous recent events.

Maximum temperature

Above average maximum temperatureswere observed in much of western, central
and southeastern WA in June 2012 , with areas of up to 3 °C warmer than
normal in the western Interior. Below average daytime temperatures were mainly
confined to the east Kimberley where temperatures were up to 2 °C cooler
than normal.

When averaged across the state as a whole, the mean maximum temperature for
WA during June 2012 was near average, whilst for the Lower Southwest, daytime
temperatures were also near average. The Lower Southwest has experienced a very
warm first half of 2012. The mean maxima for the first six months (January to
June ) was 0.9 °C above normal and ranked the 5th warmest January - June
period on record, largely due to an above average January and a very warm autumn
(the 5th warmest). Comparable temperature records commenced in 1950. This "warm"
run of temperatures has persisted for almost three years as the Lower West has
only recorded two below average months, in terms of maximum temperature, since
September 2009.

A trough inland from the west coast and a high to the south of the state brought
a very warm day to the eastern Central Wheat Belt on the 2nd, with a daily maxima
in mid-twenties. Narembeen registered its warmest June day in 41 years of record,
with a maximum temperature of 25.9 °C, exceeding the previous record of
25.4 °C set on 7 June 1988. Conversely, the coldest day of the month was
the 13th when a deep low brought a cold airmass over the SWLD, with daily maxima
barely over 10 °C in the southern parts of the SWLD. Snow fell on Bluff
Knoll in the Stirling Ranges in the South Coastal district on the morning and
early afternoon of the 13th.

Minimum temperature

June 2012 saw below to very much below average minimum temperatures in northern
and eastern parts of WA, with overnight temperatures up to 5 °C cooler than
normal in the far northeast Kimberley. Western parts of WA, from the west Pilbara
to the South Coastal, reported above to very much above average mean minimum
temperatures, with areas up to 2 °C warmer than normal in the southwest
Gascoyne and much of Central West.

When averaged across the state as a whole, the June 2012 mean minimum temperature
was near average, whilst the Lower Southwest observed above average overnight
temperatures. Comparable records commenced in 1950.

Cloudy skies and northerly winds in the western parts of the state brought
a warm night to the southwest Pilbara on the 10th, and western Central West
on the 11th, with Emu Creek Station and Kalbarri observing their warmest June
nights on record on the 10th and 11th respectively.

During the first half of 2012, WA as a whole has observed its 7th coolest January
to June period on record in terms of minimum temperature, with each of the first
six months this year seeing a cooler than normal minimum. In contrast, the Lower
Southwest has observed its 8th warmest start to the year on record, with May
being the only month to record a below average monthly minimum. In fact the
warm conditions have persisted for almost two years in the Lower West as May
2012 has been the only below average month for the region since October 2010.

Other Phenomena

A trough off the west coast of the SWLD associated with a low southwest of
the state produced severe thunderstorms over the Lower West and neighbouring
districts in the late morning and early afternoon on the 7th. Tornadoes struck
the suburbs of Dianella and Morley in Perth, and near York in the Central Wheat
Belt, causing significant damage to homes and businesses as 5000 properties
lost power. The tornadoes were the result of non-cold front related severe thunderstorms,
which are highly unusual in southwest WA in winter.

Notes

A Monthly Climate Summary is prepared to list the main features of the weather in Western Australia using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at
10 am on Monday 2 July 2012.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

Averages are long-term means based on observations from all available
years of record, which vary widely from site to site. They are not shown for
sites with less than 10 years of record.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.

Records in this summary are based on sites with at least 30 years of data.

For PDF files of Perth Metro climate statistics for other months, please click
here
for extremes and
here
for averages.